scholarly journals δD – δ18O Relationships in Ice Formed by Subglacial Freezing: Paleoclimatic Implications

1985 ◽  
Vol 31 (109) ◽  
pp. 229-232 ◽  
Author(s):  
R. A. Souchez ◽  
J. M. de Groote
Keyword(s):  
Computer Simulation ◽  
Isotopic Composition ◽  
Ice Sheets ◽  
Ice Cores ◽  
System Model ◽  
Polar Ice ◽  
Bottom Part ◽  
Basal Ice ◽  
Polar Ice Sheets ◽  
Glacier Ice

AbstractA freezing slope, distinct from that of precipitation, is displayed on a δD–δ18O diagram by basal ice in different circumstances. However, if the subglacial reservoir allowed to freeze is mixed in the course of time with an input having a lighter isotopic composition, basal ice cannot be distinguished from glacier ice in terms of slope. Such a situation is encountered at the base of Grubengletscher and is indicated by a computer simulation using the open-system model of Souchez and Jouzel (1984). Suggested implications for the paleoclimatic interpretation of deep ice cores recovered from the bottom part of polar ice sheets are given.

δD – δ18O Relationships in Ice Formed by Subglacial Freezing: Paleoclimatic Implications

1985 ◽  
Vol 31 (109) ◽  
pp. 229-232 ◽  
Author(s):  
R. A. Souchez ◽  
J. M. de Groote
Keyword(s):  
Computer Simulation ◽  
Isotopic Composition ◽  
Ice Sheets ◽  
Ice Cores ◽  
System Model ◽  
Polar Ice ◽  
Bottom Part ◽  
Basal Ice ◽  
Polar Ice Sheets ◽  
Glacier Ice

AbstractA freezing slope, distinct from that of precipitation, is displayed on a δD–δ18O diagram by basal ice in different circumstances. However, if the subglacial reservoir allowed to freeze is mixed in the course of time with an input having a lighter isotopic composition, basal ice cannot be distinguished from glacier ice in terms of slope. Such a situation is encountered at the base of Grubengletscher and is indicated by a computer simulation using the open-system model of Souchez and Jouzel (1984). Suggested implications for the paleoclimatic interpretation of deep ice cores recovered from the bottom part of polar ice sheets are given.

scholarly journals Characteristics of bubble volumes in firn-ice transition layers of ice cores from polar ice sheets

1994 ◽  
Vol 20 ◽  
pp. 95-100
Author(s):  
Takao Kameda ◽  
Renji Naruse
Keyword(s):  
Bulk Density ◽  
Classical Method ◽  
Accumulation Rate ◽  
Bubble Formation ◽  
Ice Sheets ◽  
Ice Cores ◽  
Ideal Gas ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
Glacier Ice

The air-bubble formation process has been studied experimentally by using five ice cores from the Greenland and Antarctic ice sheets. Bubble volumes in firn-ice samples were measured by a classical method based on Boyle Mariotte's law for an ideal gas. It was found that the bubble volume varies with depth as a function of bulk density in the firn-ice transition layer, which is represented by an exponential function of firn density. Air bubbles start to form rapidly at a bulk density of 0.763–0.797 Mg m-3. This density (ρib) seems to be correlated with the ice temperature in the ice sheets; ρibincreases with a decrease in the ice temperature. Vbshows the maximum value in the density range 0.819–0.832 Mg m-3. The corresponding porosity of the density ranges between 0.110 and 0.097. This porosity does not seem to correlate with ice temperature or accumulation rate at the coring site. These characteristics of firn densities probably affect the amount of entrapped air in glacier ice (total air content) in polar ice sheets.

scholarly journals Characteristics of bubble volumes in firn-ice transition layers of ice cores from polar ice sheets

1994 ◽  
Vol 20 ◽  
pp. 95-100
Author(s):  
Takao Kameda ◽  
Renji Naruse
Keyword(s):  
Bulk Density ◽  
Classical Method ◽  
Accumulation Rate ◽  
Bubble Formation ◽  
Ice Sheets ◽  
Ice Cores ◽  
Ideal Gas ◽  
Polar Ice ◽  
Polar Ice Sheets ◽  
Glacier Ice

The air-bubble formation process has been studied experimentally by using five ice cores from the Greenland and Antarctic ice sheets. Bubble volumes in firn-ice samples were measured by a classical method based on Boyle Mariotte's law for an ideal gas. It was found that the bubble volume varies with depth as a function of bulk density in the firn-ice transition layer, which is represented by an exponential function of firn density. Air bubbles start to form rapidly at a bulk density of 0.763–0.797 Mg m-3. This density (ρib) seems to be correlated with the ice temperature in the ice sheets; ρib increases with a decrease in the ice temperature. Vb shows the maximum value in the density range 0.819–0.832 Mg m-3. The corresponding porosity of the density ranges between 0.110 and 0.097. This porosity does not seem to correlate with ice temperature or accumulation rate at the coring site. These characteristics of firn densities probably affect the amount of entrapped air in glacier ice (total air content) in polar ice sheets.

scholarly journals The Theory of Thermal Convection in Polar Ice Sheets

1976 ◽  
Vol 16 (74) ◽  
pp. 41-71 ◽  
Author(s):  
T.J. Hughes
Keyword(s):  
Thermal Convection ◽  
Critical Rayleigh Number ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Transient Creep ◽  
Steady State Creep ◽  
Polar Ice ◽  
Ice Streams ◽  
Basal Ice ◽  
Polar Ice Sheets

Abstract Application of thermal convection theory to polar ice sheets (Hughes, 1970, 1971. 1972[a],[c]) is reviewed and expanded. If it occurs, thermal convection is mainly concentrated near the bed of the ice sheet; resulting in active and passive convective flow, respectively below and above the ice density inversion. Convection begins as transient creep when a stress-independent critical Rayleigh number is exceeded, and stabilizes as steady-state creep when a stress-dependent critical Rayleigh number is exceeded. Transient- creep convection begins as unstable ripples in isotherms near the bed, with some ripples becoming upward bulges of basal ice which rapidly shrink laterally and grow vertically to become ascending dikes of recrystallized basal ice during steady-state creep. Sills of basal ice are injected horizontally between weakly coupled layers in the strata of cold ice slowly sinking en masse between dikes. Convection begins under domes of thick ice toward the ice-sheet center and a stable polygonal array of dikes may form if frictional heat creates hot ice at the bed as rapidly as convection flow redistributes hot basal ice in dikes and sills, Advective flow transports the converting ice toward the margin of the ice sheet where dikes converge at the heads of ice streams. Dike—sill convection then becomes ice-stream convection in which the entire ice stream behaves like a dike, uncoupling from the bed, and rising en masse. This would help explain why ice streams flow at surge velocities.

scholarly journals Laboratory studies of the flow rates of debris-laden ice

2003 ◽  
Vol 37 ◽  
pp. 108-112 ◽  
Author(s):  
Tim H. Jacka ◽  
Shavawn Donoghue ◽  
Jun Li ◽  
William F. Budd ◽  
Ross M. Anderson
Keyword(s):  
Laboratory Tests ◽  
Ice Sheets ◽  
Ice Sheet ◽  
Laboratory Studies ◽  
Polar Ice ◽  
Flow Rates ◽  
Basal Ice ◽  
Ice Flows ◽  
Polar Ice Sheets ◽  
Deformation Tests

AbstractIce-sheet basal ice is warmer than that above because of the heat from the Earth’s interior. The stresses acting on the basal ice are greatest. In addition, the basal ice often contains debris consisting of silt and small stones picked up from the rock over which the ice flows. Because the base is the warmest part of an ice sheet and the stress there is greatest, flow rates in the basal ice are large and often contribute most of the ice movement. It is therefore important, for accurate modelling of the ice sheets, to know whether the debris within the basal ice enhances or retards the flow of the ice. In this paper, we describe laboratory deformation tests in uniaxial compression and in simple shear, on sand-laden ice. We find no significant dependence of flow rate on sand content (up to 15% volume) in the stress range 0.13–0.5 MPa and temperature range –0.02 to –18.0°C. Further work needs to include laboratory tests on debris-laden ice extracted from the polar ice sheets. This work is underway.

scholarly journals Deformation and recrystallization processes of ice from polar ice sheets

2000 ◽  
Vol 30 ◽  
pp. 83-87 ◽  
Author(s):  
Paul Duval ◽  
Laurent Arnaud ◽  
Olivier Brissaud ◽  
Maureen Montagnat ◽  
Sophie de la Chapelle
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Migration ◽  
Ice Sheets ◽  
Ice Cores ◽  
Grain Boundary Sliding ◽  
Tertiary Creep ◽  
Dislocation Slip ◽  
Polar Ice ◽  
Polar Ice Sheets

AbstractInformation on deformation modes, fabric development and recrystallization processes was obtained by study of deep ice cores from polar ice sheets. It is shown that intracrystalline slip is the main deformation mechanism in polar ice sheets. Grain-boundary sliding does not appear to be a significant deformation mode. Special emphasis was laid on the occurrence of "laboratory" tertiary creep in ice sheets. The creep behavior is directly related to recrystallization processes. Grain-boundary migration associated with grain growth and rotation recrystallization accommodates dislocation slip and counteracts strain hardening. The fabric pattern is similar to that induced only by slip, even if rotation recrystallization slows down fabric development. Fabrics which develop during tertiary creep, and are associated with migration recrystallization, are typical recrystallization fabrics. They are associated with the fast boundary migration regime as observed in temperate glaciers. A decrease of the stress exponent is expected from 3, when migration recrystallization occurs, to a value ≤ 2 when normal grain growth occurs.

scholarly journals Snow Stratigraphic Studies At Dome C, East Antarctica: An Investigation Of Depositional and Diagenetic Processes

1982 ◽  
Vol 3 ◽  
pp. 239-242 ◽  
Author(s):  
J. M. Palais ◽  
I. M. Whillans ◽  
C. Bull
Keyword(s):  
Ice Sheets ◽  
Ice Cores ◽  
Snow Accumulation ◽  
East Antarctica ◽  
Polar Ice ◽  
Depositional Processes ◽  
Diagenetic Processes ◽  
Snow Stratigraphy ◽  
Stratigraphic Record ◽  
Polar Ice Sheets

The increased interest in past climatic changes, as revealed by studies of long ice cores from polar ice sheets, has stressed the need for a better understanding of the development of the stratigraphic record preserved in these cores. This paper presents some results of surface investigations at Dome C (74°30'S, 123°10'E), East Antarctica, carried out in austral summers 1978-79 and 1979-80. An explanation is presented of the snow stratigraphy, in terms of depositional and post-depositional processes, that is supported by detailed accumulation measurements at stakes and by snow-pit studies. Temporal and areal variability of snow accumulation are investigated to determine how representative the results interpreted from a single core might be for the Dome C region. Finally, the reliability of several stratigraphic methods for defining annual layers is assessed.Snow-pit studies show that major depositional features are preserved with depth. Visible annual strata at Dome C are composed of thin, hard crusts overlying thicker layers of soft to medium-hard snow. Low density depth-hoar layers, when they occur, are usually found below the thin, hard crusts. Depth profiles of gross 8-radioactivity and of microparticles concentration exhibit annual cyclicity which, together with the detailed visible stratigraphy, can be used to assign dates to the layers.

scholarly journals Post-drilling recrystallization of the Byrd Station deep ice core and its relevance to current and future deep-core drilling on polar ice sheets

1994 ◽  
Vol 20 ◽  
pp. 231-236
Author(s):  
A.J. Gow
Keyword(s):  
Ice Core ◽  
Ice Sheets ◽  
Ice Cores ◽  
The United States ◽  
Polar Ice ◽  
Thin Sections ◽  
Full Extent ◽  
Drill Site ◽  
Polar Ice Sheets ◽  
Highly Strained

Cores of highly strained ice recovered from depths of 1200–1800 m at Byrd Station in 1967–68 have been found to have recrystallized while in storage in the United States. Such recrystallization, inferred to have occurred when temperatures in the storage facility rose above about – 14°C, would not have been discovered if thin sections of the cores had not been prepared and photographed at the drill site within hours of pulling the cores to the surface. It was only after new sections of the long stored cores were compared with the original sections that the full extent of recrystallization was revealed. The recrystallized structure emulates in both texture and fabric those observed in naturally annealed ice in the bottom 350 m at Byrd Station. It is concluded that polar ice cores should be stored at temperatures of –20°C or colder in order to inhibit or minimize post-drilling recrystallization.

scholarly journals A Review of the Microstructural Location of Impurities in Polar Ice and Their Impacts on Deformation

2021 ◽  
Vol 8 ◽  
Author(s):  
Nicolas Stoll ◽  
Jan Eichler ◽  
Maria Hörhold ◽  
Wataru Shigeyama ◽  
Ilka Weikusat
Keyword(s):  
Deformation Behaviour ◽  
Ice Core ◽  
Measurement Techniques ◽  
Ice Sheets ◽  
Ice Cores ◽  
Holistic Approach ◽  
Triple Junctions ◽  
Polar Ice ◽  
Theoretical Approaches ◽  
Polar Ice Sheets

Insoluble and soluble impurities, enclosed in polar ice sheets, have a major impact on the deformation behaviour of the ice. Macro- and Micro-scale deformation observed in ice sheets and ice cores has been retraced to chemical loads in the ice, even though the absolute concentration is negligible. And therefore the exact location of the impurities matters: Allocating impurities to specific locations inside the ice microstructure inherently determines the physical explanation of the observed interaction between chemical load and the deformational behaviour. Both, soluble and non-soluble impurities were located in grain boundaries, triple junctions or in the grain interior, using different methods, samples and theoretical approaches. While each of the observations is adding to the growing understanding of the effect of impurities in polar ice, the growing number of ambiguous results calls for a dedicated and holistic approach in assessing the findings. Thus, we here aim to give a state of the art overview of the development in microstructural impurity research over the last 20 years. We evaluate the used methods, discuss proposed deformation mechanisms and identify two main reasons for the observed ambiguity: 1) limitations and biases of measurement techniques and 2) the physical state of the analysed impurity. To overcome these obstacles we suggest possible approaches, such as the continuous analysis of impurities in deep ice cores with complementary methods, the implementation of these analyses into established in-situ ice core processing routines, a more holistic analysis of the microstructural location of impurities, and an enhanced knowledge-transfer via an open access data base.

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